broadband-modem: fall back to +CSQ if +CIND reports no signal

This is the port to git master of the following commit:

commit 8bd6903c30e52e65a4afbebf85ba59e6c0fada71
Author: Dan Williams <dcbw@redhat.com>
Date:   Thu Oct 4 09:34:01 2012 -0500

    gsm: fall back to +CSQ if +CIND reports no signal (bgo #636040)

    Some devices say they support +CIND signal reporting, but either
    actually don't, or they report signal for a non-current access
    technology that we don't care about.  So if +CIND reports zero
    signal, fall back to +CSQ.

src/mm-broadband-modem.c

@@ -1424,28 +1424,19 @@ signal_quality_cind_ready (MMBroadbandModem *self,
     GError *error = NULL;
     const gchar *result;
     GByteArray *indicators;
+    guint quality;
 
     result = mm_base_modem_at_command_finish (MM_BASE_MODEM (self), res, &error);
     if (!error)
         indicators = mm_3gpp_parse_cind_read_response (result, &error);
 
-    if (error)
+    if (error) {
         g_simple_async_result_take_error (ctx->result, error);
-    else if (indicators->len >= self->priv->modem_cind_indicator_signal_quality) {
+        signal_quality_context_complete_and_free (ctx);
-        guint quality;
+        return;
+    }
 
-        quality = g_array_index (indicators,
+    if (indicators->len < self->priv->modem_cind_indicator_signal_quality) {
-                                 guint8,
-                                 self->priv->modem_cind_indicator_signal_quality);
-        quality = normalize_ciev_cind_signal_quality (quality,
-                                                      self->priv->modem_cind_min_signal_quality,
-                                                      self->priv->modem_cind_max_signal_quality);
-        g_simple_async_result_set_op_res_gpointer (ctx->result,
-                                                   GUINT_TO_POINTER (quality),
-                                                   NULL);
-
-        g_byte_array_free (indicators, TRUE);
-    } else
         g_simple_async_result_set_error (ctx->result,
                                          MM_CORE_ERROR,
                                          MM_CORE_ERROR_FAILED,
@@ -1453,7 +1444,32 @@ signal_quality_cind_ready (MMBroadbandModem *self,
                                          "signal index (%u) outside received range (0-%u)",
                                          self->priv->modem_cind_indicator_signal_quality,
                                          indicators->len);
+        g_byte_array_free (indicators, TRUE);
+        signal_quality_context_complete_and_free (ctx);
+        return;
+    }
 
+    quality = g_array_index (indicators,
+                             guint8,
+                             self->priv->modem_cind_indicator_signal_quality);
+    g_byte_array_free (indicators, TRUE);
+
+    quality = normalize_ciev_cind_signal_quality (quality,
+                                                  self->priv->modem_cind_min_signal_quality,
+                                                  self->priv->modem_cind_max_signal_quality);
+
+    /* Some LTE devices say they support signal via CIND,
+     * but always report zero even though they have signal.  So
+     * if we get zero signal, try CSQ too.  (bgo #636040)
+     */
+    if (quality == 0) {
+        signal_quality_csq (ctx);
+        return;
+    }
+
+    g_simple_async_result_set_op_res_gpointer (ctx->result,
+                                               GUINT_TO_POINTER (quality),
+                                               NULL);
     signal_quality_context_complete_and_free (ctx);
 }